共查询到20条相似文献,搜索用时 218 毫秒
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应用蒙特卡罗方法求解几何因子,基于蒙特卡罗方法的几何因子计算程序使用C++语言编写,可用于任意位姿的各种尺寸的圆面探测器对圆面源几何因子的计算。该程序使用了方差减小技巧。通过与国际通用蒙特卡罗计算程序(MCNP5)的计算结果对比,该方法具有结果准确(误差较小)、计算速度快、使用方便等优点。最终使用该程序计算几何因子,与实验数据进行对比,成功验证了中子深度分布分析(NDP)能谱测量系统探测器位姿的准确性(误差5%以内),并对其移动位置进行修正,发现电机移动20mm大约会产生1mm的误差。 相似文献
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为了用蒙特卡罗方法计算各种复杂几何核系统的有效增殖因子(Keff),本工作给出了一种适于在复杂几何核系统内进行随机游动的方法,并用这一方法建立了相应的FORTRAN程序。 相似文献
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用蒙特卡罗方法计算三维多孔隙度测井问题是一种比较有效的方法。本文给出增加了重新启动功能的MORSE-CG[1]多功能蒙特卡罗程序计算孔隙度分别为1.0%和20.0%的基准中子测井问题的计算结果,以及其与MCNP和McDNL计算结果和计算时间的比较。比较显示三者在相同误差范围内的结果是一致的。 相似文献
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一、引言 苏联的库尔恰托夫研究所最早报导了强流相对论电子束与等离子体相互作用过程中能量沉积的磁增强效应,该所于1976年发表了实验结果,增强因子是10;随后美国的Sandia实验室报导的磁增强因子是2—5;C.Peugnet和R.Bailly-Salins等人用强流电子束在薄金靶上做实验,获得了2—3倍的增强效应。他们的实验结果与理论计算结果是相符合的。本文主要是用蒙特卡罗方法对电子束在束自磁场的作用下的运动进行了模拟跟踪,计算了电子在薄铜靶中沉积能量的磁增强效应。 相似文献
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为克服蒙特卡罗(MC)方法计算时间长和离散纵标(SN)方法复杂几何描述不精确的困难,采用SN-MC耦合计算流程,研究了基于蒙特卡罗方法和离散纵标方法的耦合方法。耦合方法的主要思想是根据离散纵标程序提供的中子角通量,利用接口程序计算出面源的分布概率,然后由修改后的源抽样子程序生成包括上下圆面源和圆柱面源的组合源,提供给蒙特卡罗程序进行计算分析。初步计算结果表明,该耦合方法是正确的,可用于压水堆堆腔漏束的计算分析。 相似文献
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对于深穿透问题则一般蒙特卡罗方法存在一定的困难。本文提出了一个新的蒙特卡罗计算深穿透问题的小区域方法。在此基础上给出了两个小区域方法,即平几何小区域方法和球几何小区域方法,通过例子的实际计算表明,小区域方法是比较好的和可行的,克服了一般蒙特卡罗方法解深穿透问题的缺点。 相似文献
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A. Jagannathan 《The European Physical Journal B - Condensed Matter and Complex Systems》2012,85(2):68
We describe some of the properties of 2d quantum quasiperiodic antiferromagnets as reported in studies that have been carried
out in the last decade. Many results have been obtained for perfectly ordered as well as for disordered two dimensional bipartite
quasiperiodic tilings. The theoretical methods used include spin wave theory, and renormalization group along with Quantum
Monte Carlo simulations. These methods all show that the ground state of these unfrustrated antiferromagnets have Néel type
order but with a highly complex spatial distribution of local staggered magnetization. The ground state properties, excitation
energies and spatial dependence, structure factor, and local susceptibilities are presented and discussed. The effects of
introducing geometrical disorder on the magnetic properties are discussed. 相似文献
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An intrinsic measure of the quality of a variational wave function is given by its overlap with the ground state of the system. We derive a general formula to compute this overlap when quantum dynamics in imaginary time is accessible. The overlap is simply related to the area under the E(tau) curve, i.e., the energy as a function of imaginary time. This has important applications to, for example, quantum Monte Carlo simulations where the overlap becomes as a simple by-product of routine simulations. As a result, we find that the practical definition of a good variational wave function for quantum Monte Carlo simulations, i.e., fast convergence to the ground state, is equivalent to a good overlap with the actual ground state of the system. 相似文献
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Green's function Monte Carlo method combined with restricted Boltzmann machine approach to the frustrated J1-J2 Heisenberg model 下载免费PDF全文
Restricted Boltzmann machine (RBM) has been proposed as a powerful variational ansatz to represent the ground state of a given quantum many-body system. On the other hand, as a shallow neural network, it is found that the RBM is still hardly able to capture the characteristics of systems with large sizes or complicated interactions. In order to find a way out of the dilemma, here, we propose to adopt the Green's function Monte Carlo (GFMC) method for which the RBM is used as a guiding wave function. To demonstrate the implementation and effectiveness of the proposal, we have applied the proposal to study the frustrated J1-J2 Heisenberg model on a square lattice, which is considered as a typical model with sign problem for quantum Monte Carlo simulations. The calculation results demonstrate that the GFMC method can significantly further reduce the relative error of the ground-state energy on the basis of the RBM variational results. This encourages to combine the GFMC method with other neural networks like convolutional neural networks for dealing with more models with sign problem in the future. 相似文献
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Validation of the Ability of Full Configuration Interaction Quantum Monte Carlo for Studying the 2D Hubbard Model 下载免费PDF全文
《中国物理快报》2017,(8)
To validate the ability of full configuration interaction quantum Monte Carlo(FCIQMC) for studying the 2 D Hubbard model near half-filling regime, the ground state energies of a 4 x 4 square lattice system with various interaction strengths are calculated. It is found that the calculated results are in good agreement with those obtained by exact diagonalization(i.e., the exact values for a given basis set) when the population of psi particles(psips) is higher than the critical population required to correctly sample the ground state wave function. In addition, the variations of the average computational time per 20 Monte Carlo cycles with the coupling strength and the number of processors are also analyzed. The calculated results show that the computational efficiency of an FCIQMC calculation is mainly affected by the total population of psips and the communication between processors. These results can provide useful references for understanding the FCIQMC algorithm, studying the ground state properties of the 2 D Hubbard model for the larger system size by the FCIQMC method and using a computational budget as effectively as possible. 相似文献
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In this paper, the ground state wave function of four parameters is developed and the expression of the ground state level is derived for the helium atom when the radial
Schrödinger equation of the
helium atom is solved. The ground energy is respectively computed by the
optimized algorithms of Matlab 7.0 and the Monte Carlo methods. Furthermore,
the ground state wave function is obtained. Compared with the experiment
value and the value with the variation calculus in reference, the results of
this paper show that in the four-parameter scheme, not only the
calculations become more simplified and precise, but also the radial wave
function of the helium atom meets the space symmetry automatically in ground state. 相似文献
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The ground-state energies and pairing gaps in dilute superfluid Fermi gases have now been calculated with the quantum Monte Carlo method without detailed knowledge of their wave functions. However, such knowledge is essential to predict other properties of these gases such as density matrices and pair distribution functions. We present a new and simple method to optimize the wave functions of quantum fluids using the Green's function Monte Carlo method. It is used to calculate the pair distribution functions and potential energies of Fermi gases over the entire regime from atomic Bardeen-Cooper-Schrieffer superfluid to molecular Bose-Einstein condensation, spanned as the interaction strength is varied. 相似文献
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S. Panda B. K. Panda 《The European Physical Journal B - Condensed Matter and Complex Systems》2010,76(2):187-196
In the fractional dimensional space, the ground state properties
of the charged-boson fluid
are studied in a theory which goes beyond the random
phase approximation by including correlations through
a static local-field-factor. The structure factor and static
local field-factor
are obtained in
the self-consistent method.
Qualitative agreement with
the Monte Carlo results on static screening is achieved
by imposing self-consistency
on the compressibility of the fluid in addition to self-consistency
on the structure factor.
Using the structure
factors obtained in these methods, several properties
of the charged boson system such as the energy spectrum of elementary
excitations, the pair-correlation function,
the ground state energy,
the pressure,
the chemical potential and the compressibility are obtained in several
dimensions including both integer and fractional values.
Results obtained in the later method in two and three dimensional
systems are close to the Monte Carlo and hypernetted-chain methods.
The Wigner crystallisation in the lower dimensional system is found at
higher density of bosons. However, it vanishes
in any lower dimensional system whose dimension lies below 2. 相似文献
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We have proposed a novel numerical method to calculate accurately physical quantities of the ground state using the tensor network wave function in two dimensions. The tensor network wave function is determined by an iterative projection approach which uses the Trotter-Suzuki decomposition formula of quantum operators and the singular value decomposition of matrix. The norm of the wave function and the expectation value of a physical observable are evaluated by a coarse-grain tensor renormalization group approach. Our method allows a tensor network wave function with a high bond degree of freedom (such as D=8) to be handled accurately and efficiently in the thermodynamic limit. For the Heisenberg model on a honeycomb lattice, our results for the ground state energy and the staggered magnetization agree well with those obtained by the quantum Monte Carlo and other approaches. 相似文献
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Z.X. CaoY.L. Ye J. XiaoL.H. Lv D.X. JiangT. Zheng H. HuaZ.H. Li X.Q. LiY.C. Ge J.L. LouR. Qiao Q.T. LiH.B. You R.J. ChenD.Y. Pang H. SakuraiH. Otsu M. NishimuraS. Sakaguchi H. BabaY. Togano K. YonedaC. Li S. WangH. Wang K.A. LiT. Nakamura Y. NakayamaY. Kondo S. DeguchiY. Satou K. Tshoo 《Physics letters. [Part B]》2012,707(1):46-51
We report for the first time the discrimination of the core fragment knockout and valence nucleon knockout reaction mechanisms at medium energy range, by the use of the recoil proton tagging technique. Intense 8He beams at 82.3 MeV/u were supplied by the RIPS beam line at RIKEN, and impinged on both hydrogen and carbon targets. Recoil protons were detected in coincidence with the forward moving core fragments and neutrons. The core fragment knockout mechanism is identified through the polar angle correlation and checked by various kinematics relations. This mechanism may be used to extract the cluster structure information of unstable nuclei. On the other hand, with the selection of the tagged valence nucleon knockout mechanism, a narrower peak of 7He ground state is obtained. The extracted neutron spectroscopic factor Sn=0.512(18) is relatively smaller than the no-tagged one, and is in good agreement with the prediction of ab initio Green?s function Monte Carlo calculations. 相似文献